The oil pump is attached to the crankcase by 4 threaded ends. To dismantle the oil pump, it is advisable to remove the threaded ends so that the oil pump extractor can be used to extract the oil pump without damage.
It's easiest to remove the threaded ends by turning two nuts on top of each other, then unscrewing the threaded end using the lower nut. If the assembly is very tight, this is not without risk: the risk of damaging the thread is present and reinstalling a damaged threaded end is the wrong choice; replacing it is the only correct way.
These threaded nipples were not only used for the oil pump on the engines mentioned, but also to hold the crankcase halves together on Type 4 engines (above and below the camshaft plug at the front of the engine, flywheel side).
They were also used in the clutch of the semi-automatic gearbox on the Volkswagen Beetle and Karmann Ghia, and for the cylinder head exhaust system on the VW Split Bus until June 1959. The latter is rather unusual, as it's not the case on the Beetle and Karmann Ghia, which share the same engines. The threaded ends are 38 mm, i.e. 4 mm smaller.
To be clear, these are not standard studs. They have a hardness of 10.9 and a length of 42 mm, making them unique in their kind, so they cannot be replaced by other studs with a different hardness or length.
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